[time-nuts] UPS for my time rack

Brooke Clarke brooke at pacific.net
Tue Oct 13 16:28:59 EDT 2015

Hi Tom:

The Li-Ion 18650 size cells (18mm dia x 650mm long) are used in most laptop computer batteries and Tesla cars because 
they are made in such high volumes.
The referenced article shows a single 18650 cell, but with about 3.7 Volts per cell you need to connect them in series 
and/or parallel to get the typically needed 12 or 24 Volts (and needed amp hours) for backup power.  The big problem is 
these cells can easily catch on fire and/or explode if they are mistreated either during discharge or charge.  To 
prevent that a protection circuit needs to be incorporated for each individual cell.  The easiest way to do that is to 
buy a battery pack with internal protection circuits and matched charger.  Then this can be connected to the external DC 
input on an individual piece of equipment.  For example:
My first precision oscillator was a rack mount Gibbs 5 MHz standard that I got for a very low price because the internal 
lead acid battery had vented acid fumes which etched away many of the copper PCB traces inside the oven.
Mail_Attachment --
Have Fun,

Brooke Clarke
Tom Van Baak wrote:
> I found this UPS article fascinating, because it echoed what I eventually found in my own lab:
> http://www.theplatform.net/2015/03/13/how-this-battery-cut-microsoft-datacenter-costs-by-a-quarter/
> I used to rely on one massive UPS (along with natural gas generator) for my entire lab. Eventually I found it more reliable and convenient to have localized power backup. By local I mean backup for a single shelf, or even a single instrument.
> Consider that many Rb/Cs standards and even some Qz standards have internal batteries. Even if one chooses not to use their internal batteries, most of these instruments still feature dual power inputs. In addition to power redundancy it also makes it easy to move equipment or cables around without power loss. Most importantly, local backup like this avoids the possibility of single-point lab-wide power failures.
> Recently, as some of my gear works from 5 VDC, those ~2600 mAh mobile phone USB backup power bricks make an excellent mini-UPS. The ideal models are those without LEDs or on/off buttons so they discharge and charge/float seamlessly without manual intervention, even if fully drained.
> Multiple units can be placed in series for additional, if slightly inefficient, capacity. A good self-test is:
> http://leapsecond.com/images/perpetual-USB-power.jpg
> /tvb
> ----- Original Message -----
> From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>; "Bill Byrom" <time at radio.sent.com>
> Sent: Monday, October 12, 2015 11:44 PM
> Subject: Re: [time-nuts] UPS for my time rack
>> --------
>> In message <1444701906.379459.408467601.5676DFA5 at webmail.messagingengine.com>,
>> Bill Byrom writes:
>>> Anything can (and will) fail, [...]
>> The interesting thing is that several sources in that business have
>> reported to me that about 30-40% of all power related downtime is
>> caused by Battery, generator and UPS failure, in that order.
>> Many sites simply have lower uptime after they install UPS systems.
>> -- 
>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>> FreeBSD committer       | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by incompetence.
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